1. Field of the Invention
The present invention is a unique automotive powertrain design that allows highly efficient use of energy generated by an integrated internal combustion engine. Field of application is in automotive powertrains.
2. The Prior Art
The growing utilization of automobiles greatly adds to the atmospheric presence of various pollutants including greenhouse gases such as carbon dioxide. Current powertrains typically average only about 15% thermal efficiency. Accordingly, new approaches to improve the efficiency of fuel utilization for automotive powertrains are needed.
Conventional automotive powertrains result in significant energy loss, make it difficult to effectively control emissions, and offer limited potential for improvements in automotive fuel economy. Conventional powertrains consist of an internal combustion engine and a simple mechanical transmission having a discrete number of gear ratios. Due to the inefficiencies described below, about 85% to 90% of the fuel energy consumed by such a system is wasted as heat. Only 10%-15% of the energy is available to overcome road load, and much of this is dissipated as heat in braking.
Much of the energy loss is due to a poor match between engine power capacity and average power demand. The load placed on the engine at any given instant is directly determined by the total road load at that instant, which varies between extremely high and extremely low load. To meet acceleration requirements, the engine must be many times more powerful than average road load would require. The efficiency of an internal combustion engine varies significantly with load, being best at higher loads near peak load and worst at low load. Since the vast majority of road load experienced in normal driving is near the low end of the spectrum, the engine must operate at poor efficiency (e.g., less than 20%) much of the time, even though conventional engines have peak efficiencies in the 35% to 40% range.
Another major source of energy loss is in braking. In contrast to acceleration which requires delivery of energy to the wheels, braking requires removal of energy from the wheels. Since an internal combustion engine can only produce and not reclaim energy, and a simple gear transmission can only transmit it, a conventional powertrain is a one-way energy path. Braking is achieved by a friction braking system, which renders useless the temporarily unneeded kinetic energy by converting it to heat.
The broad variation in speed and load experienced by the engine in a conventional powertrain also makes it difficult to effectively control emissions because it requires the engine to operate at many different conditions of combustion. Operating the engine at more constant speed and/or load would allow much better optimization of any emission control devices, and the overall more efficient settings of the engine would allow less fuel to be combusted per mile traveled.
Conventional powertrains offer limited potential to bring about improvements in automotive fuel economy except when combined with improvements in aerodynamic drag, weight, and rolling resistance. Such refinements can only offer incremental improvements in efficiency, and would apply equally well to improved powertrains.
Hybrid vehicle systems have been investigated as a means to mitigate the above-described inefficiencies. A hybrid vehicle system provides a xe2x80x9cbufferxe2x80x9d between road load demand and the internal combustion engine in order to moderate the variation of power demand experienced by the engine. The buffer also allows regenerative braking because it can receive and store energy. The effectiveness of a hybrid vehicle system depends on its ability to operate the engine at peak efficiencies, on the capacity and efficiency of the buffer medium, and on the efficiency of the transmission system that transfers power to the drive wheels. Typical buffer media include electric batteries, mechanical flywheels, and hydraulic accumulators.
To use a hydraulic accumulator as the buffer, a hydraulic pump/motor is integrated into the system. The pump/motor interchangeably acts as a pump or motor. As a pump, engine power rotates a shaft that pumps hydraulic fluid to an accumulator where it is pressurized against a volume of gas (e.g., nitrogen). As a motor, the pressurized fluid is released through the unit, spinning the shaft and producing power. See, for example U.S. Pat. No. 4,223,532 issued Sep. 23, 1980 to Samual Shiber.
Other U.S. Patents disclosing such hybrid powertrains include:
Hybrid Powertrain Vehiclexe2x80x94U.S. Pat. No. 5,495,912 issued Mar. 5, 1996;
Anti-Lock Regenerative Braking Systemxe2x80x94U.S. Pat. No. 5,505,527 issued Apr. 9, 1996;
Accumulator Enginexe2x80x94U.S. Pat. No. 5,579,640 issued Dec. 3, 1996;
Lightweight, Safe Hydraulic Power System and Method of Operation Thereofxe2x80x94U.S. Pat. No. 5,507,144 issued Apr. 16, 1996; and
Continuously Smooth Transmissionxe2x80x94U.S. Pat. No. 5,887,674 issued Mar. 30, 1999.
The present invention provides an automotive powertrain including a pair of drive wheels and a hydraulic circuit including at least one accumulator for receiving hydraulic fluid, storing pressure and discharging the stored pressure. The hydraulic circuit further includes first and second pump/motors or a first hydraulic pump/motor in combination with the second hydraulic pump. The first hydraulic pump/motor, operating in its motor mode, drives the drive wheels responsive to receipt of hydraulic fluid and, in a pump mode, pumps hydraulic fluid to the accumulator responsive to braking. The second hydraulic pump or hydraulic pump/motor has a shaft fixed to the crankshaft of an internal combustion engine by which it is driven, as a pump, for pumping hydraulic fluid to at least one of the accumulator and the first hydraulic pump/motor, when the latter is operating in a motor mode. Preferably, the first and second hydraulic pumps or pumps/motors are inline piston machines or, more preferably, bent-axis piston machines.
The present invention also provides an automotive powertrain including a pair of drive wheels, an internal combustion engine with a crankshaft for power output and a hydraulic power circuit. Hydraulic power circuit includes at least one accumulator for receiving hydraulic fluid, storing pressure and discharging the stored pressure. A gear set serves to transfer power from at least one hydraulic pump/motor to the drive wheels. In a preferred embodiment, two drive hydraulic pump/motors incorporated into the hydraulic power circuit are located on opposing sides of one gear of the gear set and share a common input/output shaft having that one gear mounted thereon. These first and second hydraulic pump/motors may operate either in a motor mode to drive the pair of drive wheels through the gearshaft or in a pump mode for pumping hydraulic fluid into the accumulator responsive to braking of the drivewheels. A third hydraulic pump or pump/motor driven by the internal combustion engine serves to pump hydraulic fluid to the accumulator and/or the first and second hydraulic pump/motors to drive those pump/motors in a motor mode, thereby powering the vehicle. Again, the pumps and/or pump/motors are preferably inline piston machines and more preferably bent-axis piston machines. The third hydraulic pump or pump/motor may have a driveshaft fixed to the crankshaft of the internal combustion engine as in the above-described aspect of the invention.
The present invention also provides hydraulic control logic for control of hydraulic fluid in powertrains of the types described above. More specifically, the present invention provides an automotive powertrain including a pair of drive wheels, an internal combustion engine with power output through a crankshaft and a hydraulic drive circuit. A first pump/motor, when operating in a motor mode, serves to drive the drive wheels responsive to receipt of high pressure fluid from a high pressure line and operates in a pump mode to deliver high pressure fluid to the high pressure line responsive to braking of the drive wheels. The hydraulic circuit further includes a high pressure accumulator for receiving and discharging high pressure fluid through the high pressure line and a low pressure line and a low pressure accumulator for receiving and discharging low pressure fluid through the low pressure line. The hydraulic control logic includes first and second lines connecting, in parallel, to one side of the first pump/motor to the high pressure and low pressure lines, respectively, with the first parallel line having a first valve which opens to admit high pressure fluid from the high pressure line into the one side of the first pump/motor in forward drive. The second parallel line has a second valve which opens to admit low pressure fluid from the low pressure line to the one side of the first pump/motor in reverse drive. Third and fourth parallel lines serve to connect, in parallel, a second side of the first pump/motor to the high pressure and low pressure lines, respectively. The third parallel line has a third valve which opens to admit low pressure fluid from the low pressure line to the second side of the first pump/motor in forward drive. The fourth parallel line has a fourth valve which opens to admit high pressure fluid from the high pressure line to the second side of the first pump/motor in reverse drive. Similar control logics may be provided to control operation of the second pump/motor and, optionally, a third pump/motor. First and third pump/motors may share a common shaft with a gear of a reduction gear unit as in a feature of the present invention described above.
The present invention also provides an automotive powertrain which, as in the other aspects of the present invention includes a pair of drive wheels, an internal combustion engine with power output through a crankshaft and a hydraulic drive circuit. The hydraulic drive circuit includes high pressure and low pressure lines and a first pump/motor operable over center, in a motor mode, for driving the drive wheels responsive to receipt of high pressure fluid from the high pressure line and for operating in a pump mode to deliver high pressure fluid to the high pressure line responsive to braking of the drive wheels. The hydraulic drive circuit further includes a second pump/motor operable over center and driven by the internal combustion engine for operation in a pump mode to deliver high pressure fluid to the high pressure line. The hydraulic drive circuit also includes high pressure and low pressure accumulators and a hydraulic control logic. Here, the hydraulic control logic includes first and second parallel lines for connecting, in parallel, one side of the first pump/motor to the high pressure line and low pressure line, respectively. The first parallel line has a first valve which opens to admit high pressure fluid from the high pressure line to the one side of the first pump/motor. The second parallel line has a valve for preventing fluid flow from the high pressure line directly into the low pressure line. In this hydraulic drive circuit, a second side of the first pump/motor is connected directly to the low pressure line. The second and optionally third pump/motor are provided with similar hydraulic control logics.
The hydraulic hybrid vehicle powertrain of the present invention is a unique powertrain that performs all the functions of a conventional powertrain, but at a much higher level of energy efficiency. This novel powertrain efficiently converts the kinetic energy of the moving vehicle into potential energy when decelerating (i.e., braking) the vehicle, and this energy is stored on the vehicle for subsequent re-use. The powertrain employs a unique, integrated design of various conventional and novel components necessary for energy and cost efficient operation. Also, a unique hydraulic fluid flow circuit and unique operational control logic are utilized to achieve the full energy efficiency improvements which can be realized through this new powertrain. Many of the unique features of this new powertrain apply to electric hybrid powertrains as well.